BIOSTRATIGRAPHIC SIGNIFICANCE OF A NEW POTENTIAL KEY REFERENCE SECTION FOR THE LATEST GUADALUPIAN REEF TRAIL MEMBER OF THE BELL CANYON FORMATION (MIDDLE PERMIAN), WEST TEXAS

The Reef Trail Member (Bell Canyon Formation, Guadalupian) was established in 1999 for the “post-Lamar beds” of King (1948), the youngest unit of the Middle Permian succession in West Texas. The type section was designated in a slope setting close to the Capitan Reef near the entrance to McKittrick Canyon in Guadalupe Mountains National Park. Before its formal designation, the Reef Trail unit was recognized by many workers because of the distinctive nature of its stratigraphic succession that begins with a recessively weathering siliciclastic unit above a series of limestone beds forming the top of the Lamar Limestone Member. At the type locality, the lower part of the Reef Trail contains several debris flows bearing the fusulinacean Paraboultonia splendens and the succession ends in a series of thinly bedded silty limestone beds. The upper part of the Reef Trail Member and its contact with the Castile Formation is not exposed at the type locality, but was described from a pair of low hills nearly 2 miles from McKittrick Canyon on private land. A continuous section of the Lamar and Reef Trail members, overlain by the Castile Formation (Lopingian), has recently been discovered in the Patterson Hills west of the Guadalupe Mountains, but within the national park. Approximately 18 meters of Lamar and 42 meters of Reef Trail contain an upper Middle Permian fusulinacean succession with scarce Yabeina texana in the basal Lamar beds, abundant Reichelina lamarensis in the upper Lamar beds, and Paraboultonia splendens/Codonofusiella (Lantschichites) sp. in the Reef Trail beds. The conodont Jinogondolella postserrata is present in the Lamar beds, Jinogondolella altudaensis in the Reef Trail beds, and Jinogondolella crofti with transitional forms from J. altudaensis to Clarkina postbitteri hongshuiensis (the marker for the terminal Guadalupian at the Lopingian GSSP in China) just below the basal Castile. Small recrystallized ammonoids are present at the top of the Lamar beds and at several horizons through the Reef Trail: however, none have clearly defined sutures. Radiolarians are present in the succession with Follicucullus scholasticus in the Lamar and Reef Trail members and upper Reef Trail beds containing Albaillella yamakitai, Pseudoalbaillella fusiformis, Copiellintra sp., and stauraxon radiolarians.